X-linked agammaglobulinemia (XLA) is a single gene defect characterized[unreadable] by profound hypogammaglobulinemia and markedly reduced numbers of B[unreadable] cells. The abnormal gene product has not yet been identified; however,[unreadable] studies in the Pi's laboratory have shown that the gene defect is[unreadable] intrinsic to the B cell lineage and that the gene product is likely to[unreadable] be expressed throughout B cell differentiation. In the next budget[unreadable] period the PI plans to identify, isolate and characterize the gene for[unreadable] XLA. Linkage studies have localized the gene for XLA to a 6-10 mb[unreadable] segment of the X chromosome. No recombination has been seen with the[unreadable] probe p2l2 at Xq22, suggesting that the gene defect is likely to be[unreadable] within 1-2 mb of p2l2.[unreadable] In the first specific aim, the PI will use pulse field electrophoresis,[unreadable] yeast artificial chromosomes (YACs), new DNA probes and linkage[unreadable] analysis to further refine the DNA segment within which the XLA gene[unreadable] must lie. In preliminary studies, the segment of interest has been[unreadable] trimmed to 2-3 mb by analysis of recombinant X chromosomes. The[unreadable] availability of cells and DNA from two unrelated males who are likely[unreadable] to have deletions of the XLA gene should help further localize the[unreadable] gene. YACs that encompass the XLA gene locus will be used to generate[unreadable] new DNA probes.[unreadable] In the second specific aim, the PI will identify B cell specific[unreadable] transcripts that are encoded in the XLA gene segment. The methylation[unreadable] site described above will be characterized in detail. In addition,[unreadable] phage libraries from overlapping YACs that encompass the XLA gene[unreadable] segment will be used to screen B cell cDNA libraries. In specific aim[unreadable] three, genomic DNA and/or B cell lineage mRNA from 21 unrelated[unreadable] patients with XLA will be analyzed with probes that identify XLA gene[unreadable] candidates. Identification and characterization of the XLA gene will[unreadable] undoubtedly improve diagnosis and care of affected patients. It should[unreadable] also increase our understanding of mechanisms involved in normal B cell[unreadable] differentiation.[unreadable]